This Multiple-investigator R01 research application entitled Studies of bacterial autoinducers - recognition and modulation of host processes is a collaborative effort between our group at The Scripps Research Institute (TSRI) and Dr. Kendra Rumbaugh's laboratory at Texas Tech University Health Sciences Center (TTUHSC) and brings together two leading groups in the field of host-pathogen interactions mediated by quorum sensing signaling molecules (QSSM), namely acyl homoserine lactones (AHLs). Recently published and unpublished data from our groups have demonstrated that bacterial pathogens are capable of using AHLs to modulate physiological host processes ranging from gene transcription, intracellular calcium levels, sphingolipid metabolism, and ultimately, induction of apoptosis. The overarching aim of our research effort is to comprehensively study the plethora of effects that AHLs exert on mammalian cells, elucidate the underlying molecular mechanisms, and ultimately identify the so far elusive eukaryotic AHL receptor/binding protein/recognition machinery. In this application, a combination of chemical biology, molecular biology, immunology, and genetic approaches will be harnessed to provide new insights into bacterial pathogenesis and the intricate interplay between host and pathogen. The specific aims of our R01 application are: (1) To define the impact of AHLs on inflammatory responses: In mammalian cells, pro- and anti-inflammatory activities of AHLs have been linked to alterations in gene expression regulated by the transcription factor NF-?B, although the exact mechanisms involved are poorly understood. Our hypothesis is that the dual action of AHLs is required for establishment and then maintenance of persistent infections as it modulates both early and late stages of inflammation, each of which requires NF-?B-dependent mechanisms regulated by AHL-mediated activation of the UPR. (2) To study the effect of AHLs on the sphingolipid metabolism: Our preliminary data demonstrate that AHLs affect sphingolipid metabolism. Thus, we propose to further examine the underlying molecular mechanism using a combination of cell-based approaches combined with sphingolipidomic methodologies. (3) To clarify the role of PPAR in AHL recognition and to identify additional mammalian sensor(s) for AHLs: Dr. Rumbaugh and colleagues have recently identified proteins of the peroxisome proliferator-activated receptor (PPAR) family as potential mammalian receptors of AHLs; however, PPAR-mediated signaling does not appear to account for all biochemical effects observed with AHLs, suggesting that other mammalian AHL sensors may exist. Therefore, we will pursue a two-pronged experimental approach; Dr. Rumbaugh will continue to elucidate the role of PPARs in AHL signaling, while we will use chemical biology to identify other AHL sensors that functionally link PPAR, NF-?B, and sphingolipid metabolism.